1. Field of the Invention
Embodiments of the invention are related to an apparatus and method for adjusting the current density near the perimeter of a substrate during a plating process.
2. Description of the Related Art
Metallization of high aspect ratio 90 nm and smaller sized features is a foundational technology for future generations of integrated circuit manufacturing processes. Metallization of these features is generally accomplished via an electrochemical plating process. However, electrochemical plating of these features presents several challenges to conventional gap fill methods and apparatuses. One such problem, for example, is that electrochemical plating processes generally require a conductive seed layer to be deposited onto the features to support the subsequent plating process. Conventionally, these seed layers have had a thickness of between about 1000 Å and about 2500 Å; however, as a result of the high aspect ratios of 90 nm features, seed layer thicknesses must be reduced to less than about 500 Å. This reduction in the seed layer thickness has been shown to cause a “terminal effect”, which is generally understood to be an increase in the deposition thickness of an electrochemical plating (ECP) process as a result of the current density across the surface of the substrate decreasing as the distance from the electrical contacts toward the center of the substrate increases. The impact of the decreased current density nearer the center of the substrate is that the deposition thickness near the perimeter of the substrate is substantially greater than the deposition thickness nearer the center of the substrate.
The increase in deposition thickness near the perimeter of the substrate as a result of the terminal effect presents challenges to subsequent processes, e.g., polishing, bevel cleaning, etc., and as such, minimization of the terminal effect is desired. Conventional plating apparatuses and process have attempted to overcome the terminal effect through various apparatuses and methods. For example, conventional plating cells have been modified to include active thief electrodes positioned in the wall of the plating cell. These configurations were generally unsuccessful in controlling the terminal effect as a result of their lack of proximity to the perimeter of the substrate, which resulted poor control over the deposition thickness near the perimeter. Additionally, conventional configurations have also been modified to include passive shield or flange members configured to control the terminal effect. However, these configurations were also unsuccessful, as they were generally ineffective in controlling deposition thickness near the perimeter of the substrate.
Therefore, there exists a need for an apparatus and method for adjusting the current density near the perimeter of a substrate during a plating process to overcome the terminal effect generated by thin seed layers in electrochemical plating processes.